You're blind. You're deaf. Or rather, you just see what you want to see, hear what you want to hear. If you paid any attention to the post-match interview, you would've heard the man himself say his first choice was Amoonguss (the same as any smart and reasonable Pokémon player, at least in the absence of Togekiss), and only tried Pachirisu afterwards after the overgrown mushroom yielded questionable results. This means that he didn't use Pachirisu because he had a soft spot for the thing and slapped Follow Me on it just because it's what it did better than anything else, it's because Pachirisu gave him a chance to win more matches. Yes, maybe he genuinely likes Pachirisu. But since it wasn't his first choice, it's obvious that it's not the reason why he used it. No matter how much you want to believe the opposite, he used Pachirisu the same way he would a chess piece. He applied the same logic to this whole thing as any of the Smogonites you despise oh so much. It just so happens that he picked a Pokémon that rarely sees use by most normal players in most normal environments because of the restrictions of the 2014 VGC format. So please keep your annoying "YOU CAN WIN WITH YOUR FAVORITES" bullshit at the door.
Oh, I just mentioned chess pieces. That's something else. When have you ever heard the everyday Joe complain about how Russian grandmasters are obsessed with queens? Never. That's because chess players are above that shit. Not Pokémon players, by the looks of things. You never see some scrub brag, "I always underpromote because queens are so overrated!" Yes, underpromotion is something that happens, although rarely, most often to avoid a stalemate caused by a promotion to a queen. And that's exactly what happened this weekend. Se Jun Park used a seemingly lesser option compared to Amoonguss because the latter ended up dying more often because of its relative plethora of weaknesses than because he played it badly. At that point he simply was better served by a Pokémon with only one weakness, massive loss of HP be damned. Remember how I keep saying different Pokémon can see wild fluctuations in usefulness and usage depending on the level at which it's played? When you're arguably the best player in the world, it goes double for you. Any of us regular schmoes would replace our Amoongusses with Pachirisus on the VGC ladder overnight (something I get the feeling may happen, stay tuned for monthly stats!), we'd get pulverized and left wondering, how the fuck did he do what he did?
Oh, by the way, way to conveniently forget that the rest of his team was absolutely bog standard. Guess which Pokémon Pachirisu gave a chance to molest its opponents constantly in the finals? Garchomp, the Pokémon most closely associated with what you call "self-centered stuck-up Smogon elitists"! Pachirisu, the new darling of casuals everywhere, standing next to Garchomp, Smogon's uncontested favorite (or so they say). Pretty sure the universe is about to implode. We also got such staples as Talonflame, Gyarados and Gardevoir, with only Gothitelle being slightly more exotic (but not at all a bad or uncommon choice, Shadow Tag and all).
Bottom line: the man you hail as your new hero is actually a horrible villain by your standards. But never let the truth get in the way of a good story, right?